Implantable electro-stimulation devices are commonly used today to treat patients suffering from various ailments. After implant of an implantable device for electric stimulation, such as pacemakers or Deep Brain Stimulation (DBS) devices, the device may cause heating of the device and surrounding tissue, either at the normal use of the implantable device or during scanning of the patient and device by e.g. Magnetic Resonance (MR) scanning.
The human tissue, in particular brain tissue, is sensitive to temperature raises; the maximum allowed temperature increase of brain tissue is 1° C. in that further temperature increases may have profound, negative effects on single neuron and neuronal network function. Therefore it is of concern to minimize heating effects at and around an implanted electro-stimulation device as well as to prevent undesired stimulation of the human tissue due to induced currents near the electro-stimulation device during MR scanning.
Moreover, safety and compatibility during MR scanning is of great concern for implantable electrical stimulation devices; in particular, shielding from external electromagnetic fields is important in order to avoid undesired interference of the external electromagnetic fields, e.g. RF signals. Optimum shielding effect requires the shield to be as close as possible to the electrode/electrodes of the implantable electro-stimulation device.
Furthermore, it is of concern to provide a probe for electro-stimulation wherein the stimulation is focused mainly at a region of interest and is preferably effective only at the region of interest. In order to reduce power consumption and thereby increase battery life time, a return electrode may be incorporated in the implantable electro-stimulation device in order to reduce the circuit impedance and/or provide a well defined current return path. Such a return electrode should be situated at a certain minimum distance from the electrode/electrodes of the probe in order to prevent the shunting of stimulation currents directly to the return electrode which would diminish the volume of tissue that could be excited by the stimulation currents.
WO 2008/018067 discloses a neural stimulation system using various electrode configurations and/or anodic flow to control the stimulation effect. In some embodiments, a remote cathodal collecting electrode is used. In some embodiments, a multi-polar stimulation includes anodes on either side of a cathode. WO 2008/018067 does not relate to the shielding of the system for neural stimulation against external electromagnetic fields.
Hence, an improved implantable electro-stimulation device comprising a probe with one or more electrodes would be advantageous, and in particular an electro-stimulation device with increased battery life time and/or a probe with improved shielding against external electromagnetic fields, such as RF signals, would be advantageous.